1. Field of the Invention
The present invention relates to an image processing apparatus, image processing method, program, and storage medium.
2. Description of the Related Art
A technique for implementing a copy-forgery-inhibited pattern has been disclosed (see Japanese Patent Laid-Open No. 07-231384, Japanese Patent Laid-Open No. 11-245473, Japanese Patent Laid-Open No. 2001-197297, Japanese Patent Laid-Open No. 2001-238075, and Japanese Patent Laid-Open No. 2001-324898). The copy-forgery-inhibited pattern includes a remaining region and a vanishing region. Within the remaining region, dots having a large size (to be referred to as large dots hereinafter: a size of about 160 μm 160 μm) are formed. Within the vanishing region, dots having a smaller size (to be referred to as small dots hereinafter: a size of about 42 μn 42 μm) are formed. The reflection density per unit area of the remaining region is largely similar to that of the vanishing region. In order to make the reflection densities of the two regions largely similar to each other, a relatively small number of large dots are formed on the remaining region, and a relatively large number of small dots are formed on the vanishing region.
The region where large dots are formed has the shape of the character string “invalid” or a string of similar meaning, as shown in FIG. 23. Since the reflection density per unit area of the remaining region is largely similar to that of the vanishing region, a person cannot clearly recognize the character string “invalid” or the like when viewing the copy-forgery-inhibited pattern.
When a copy is made of this copy-forgery-inhibited pattern, small dots are not accurately reproduced on the copy, while large dots are accurately reproduced. As a result, the character string “invalid” or one of similar meaning are clearly recognized by the human eye.
This copy-forgery-inhibited pattern includes blank patterns (see FIG. 23). This specification calls each such blank pattern a camouflage pattern. In FIG. 23, each camouflage pattern has a ∘ shape and, hence, the camouflage pattern is a ∘-shaped blank pattern. When the copy-forgery-inhibited pattern includes such camouflage patterns, these patterns fool the human eye, and the boundary between the remaining region and vanishing region can hardly be recognized.
A technique for embedding digital data in addition to a copy-forgery-inhibited pattern has also be disclosed (see Japanese Patent Laid-Open No. 2001-346032). Using this technique, a tracking function can be implemented simultaneously with the copy-forgery-inhibited pattern by embedding the ID of a printer or user.
Furthermore, a technique for embedding digital data on a printed document has been disclosed (see Japanese Patent No. 3628312). Although it does not make mention of a copy-forgery-inhibited patterns, Japanese Patent No. 3628312 discloses a technique for expressing information on a paper sheet, and this technique has a characteristic that two-dimensional barcodes do not have. The two-dimensional barcodes require to having a given size for expressing data. This characteristic of Japanese Patent No. 3628312 lies in the fact that digital data can be embedded such that it is superimposed on a region such as text, a table, or the like of a document. The two-dimensional barcodes do not have the characteristic.
As a known method for recognizing a boundary, character extraction based on projection or the like is known. Even when using this technique, multiple types of arranged patterns cannot be recognized. Furthermore, a character extraction technique based on projection cannot be applied to the detection of patterns from an image upon which multiple types of patterns are arranged. This is because the character extraction technique extracts characters assuming that a white pixel exists between neighboring character patterns.
A digital watermark extraction technique which is conventionally used includes three processing steps, as shown in FIG. 8. FIG. 8 is a flowchart showing the processing of the conventional digital watermark extraction technique. Referring to FIG. 8, the presence/absence of digital watermark information in input data is checked in step 801. As processing relating to determination of presence/absence of digital watermark information, statistical processing such as patchwork or the like is known. In step 802, processing for determining the embedded position of the digital watermark information is executed. In step 803, processing for extracting the digital watermark information embedded at the embedded position is executed. However, various methods for specifying the position of digital watermark information are available. In a digital watermark using camouflage of a copy-forgery-inhibited pattern, peaks may be used on a Fourier plane after a two-dimensional Fourier transformation. Finally, the digital watermark information extraction technique extracts the digital watermark information, using pattern recognition, statistical processing, and the like.
The present invention has been made in consideration of the aforementioned problems, and has as its object to provide a technique for detecting simpler the boundary of multiple types of patterns, which are arranged in a tiled fashion.